Aerials for receiving television and modulated frequency broadcast signals



Jan. 16, 1962 G. J. H. J. BERNARD 3,017,632 AERIALS FOR RECEIVING TELEVISION AND MODULATED FREQUENCY BROADCAST SIGNALS Filed Jan. '7, 1958 INVENTOR. Jib- 11- 2 4* United States Patent 3,017,632 AERIALS FOR RECEIVING TELEVISION AND 1lzlolOsULATED FREQUENCY BROADCAST SIG- My invention has for its object improvements in aerials for receiving television and modulated frequency broadcast signals, said improvements providing: the cutting out of certain losses and consequently a larger gain; a modification in the radiating diagram, in particular so as to provide a large improvement in the front to back ratio; an increase in the breadth of the range of frequencies for which the aerials may operate satisfactorily; a shortening of the aerials; the possibility of operating the aerials so as to receive broadcast signals.

Hereinafter, I will describe the invention as applied to a television aerial including three sections and I will disclose by way of comparison the measurements obtained on aerials of this type and of a conventional type.

However, it should be remarked that my invention is applicable under equally favorable results to all aerials adapted to receive television and frequency modulated broadcast signals, whatever may be the number of their elements such as dipoles, reflectors and directors and whatever may be the number of arrays forming them and it is even applicable to the execution of transmitting aerials.

A three-element television aerial includes chiefly a mast at the upper end of which is secured the medial portion of a stay, one of which carries a reflector and the other a dipole and a director.

It is assumed that the central point of the different elements carried by the stay is at a zero voltage and for this reason, without giving any further technical details, all the builders of television aerials resort to metal stays for carrying the dipole and parasitic elements such as reflectors and directors.

According to my invention, I have devised an aerial the elements of which are not considerably modified except however for the stay which is made of insulating material.

As a result of comparative tests made with an aerial having an insulated dipole and with an aerial having a non-insulated dipole, said tests being executed with various types of input windings for the television receiving sets, a substantial advantage appears in the use of insuiated dipoles as far as gain of power is concerned.

It may be thought with some reason that, generally speaking, the middle of the input winding does not form the electric middle point of the circuit. If the middle point of the dipole is grounded through the agency of the mast, this produces a lack of equilibrium of the system which leads consequently to an unequality in the current flowing through the wires of the twin cables. From this moment onwards, the electromagnetic field of one wire is no longer exactly compensated by that of the other wire so that the twin cable radiates a fraction of the energy received through the aerial and operates thus as a transmission aerial, which results in a loss the importance of which increases with the lack of equilibrium.

It should also be remarked that even if the input coil is perfectly balanced, there arises however a lack of equilibrium through the action of the aerial itself in the case of a non insulated dipole.

Owing to the variations in moisture and the action of snow or frost on the arms of the dipole, the electrical middle point is not necessarily coincident with the 3,017,632 Patented Jan. 16, 1962 "ice mechanical middle point, the latter being grounded. The different losses of power are not the sole drawbacks produced by a lack of electrical equilibrium and there should also be mentioned an important modification in the radiation diagram which modification is easily checked through a reversal of the input connections for the receiver, so that the diagram is deformed either in one direction or in the other, according to the direction of the connection of the twin cable.

These various drawbacks are removed through the insulating stays provided according to my invention, said insulating stays having a leakage line which is sufiiciently long so that it may retain excellent insulating properties even for very inclement weather conditions.

Materials which have provided good results upon testing i.e. elements which are not wettable are constituted for instance by polystyrene, Teflon and vitrified polyester resins.

A further feature of the insulated stay consists in the shortening of said stay, this being due to the fact that the coupling of the difierent elements of a television aerial, to wit the dipoles, the reflectors, and the directors is obtained chiefly through induction and also, for a fraction of the energy, through capacity.

The insulating stay reduces considerably the capacity and this may be compared with a spacing of the elements. In order to restore the original coupling, it is therefore necessary to bring the elements of the aerial nearer one another and this is important in practice since the elements are fitted laterally of the axis of the mast and are subjected to the action of the wind.

An unexpected and important feature of the invention provided through the proposed modification of the stay resides in the possibility of operating the television aerial as an excellent broadcast aerial having a terminal capacity.

This is due to the fact that the substitution of an insulating stay to the metal stay does not only reduce the electrical capacities between the different parts but also the capacity between the dipole and the mast.

Since the mast is brought through its actual arrangement to ground potential either through a direct cable connection provided for this purpose or through the unavoidable losses, said capacity between the dipole and the ground forms a direct channel for the losses of the signal energy collected by the dipole.

Said property has never been made apparent hitherto and in fact all the known arrangements lose through capacity the major part of the high frequency energy collected in the range of wireless broadcast waves, which major part leaks through the carrier insulators.

In fact, the A.R.L.L. Antenna book published by the American Radio Relay League states with reference to aerials on page 158:

As the number of parasitic elements is increased, the problem of determining the optimum element spacings and lengths to meet given specifications--i.e., maximum gain, maximum fronbto-back ratio, maximum bandwidth, and so on-becomes extremely difficult because of the large number of variables. In general, it can be said that when one of these quantitiesgain, front-to-back ratio, or bandwidth-is maximized, the other two cannot be.

Now, the measurements made by me have led me to the surprising conclusion that the aerials with an insulating stay are superior to aerials having a metal stay from the three following standpoints: gain, front to back ratio and bandwidth.

This result is thus not the consequence of a more adequate disposition of the elements, but is due to a fundamentally improved efliciency.

In the absence of any mathematic theory for the threeelement aerials taking into account the presence of a metal stay, it is impossible to provide a satisfactory quantitative explanation of the phenomenon.

I may just suggest some physical hypotheses which may explain to some extent the phenomenon in a qualitative manner.

A fraction of the useful incoming waves is reflected by some section of the metal stay instead of being absorbed by the dipoles, directors or reflectors and this leads to a loss.

Another loss could be due to the fact that a fraction of the reflected energy is sent back towards the operative elements of the aerial with a phase-difference with the direct incoming waves, so that the said fraction of the reflected energy is subtracted from the latter instead of reinforcing same.

If, according to my invention, the aerial is provided with an insulating stay, this allows selecting without any difficulty the direct waves and this is all the easier since the waves reflected on any structure, waves which it is desired to cut out, assume generally speaking, vertical polarisation which distinguishes them in all cases from the original horizontal polarisation with which they have been transmitted.

Taking into account the fact that the aerial can collect through its very structure only horizontally polarized waves, the cutting out of the undesired waves is thus obtained automatically in aerials executed in accordance with my invention.

I have illustrated diagrammatically and by way of example in the acompanying drawing a stay applied to an aerial according to my invention. The single FIGURE of said drawing is a perspective view of said stay.

In the embodiment illustrated, the stay 1 is made of insulating material and its leakage line is sufficiently long for retaining excellent insulating properties even for very inclement weather conditions.

Said stay is secured to the upper end of the mast 2 and carries the dipole 3 together with the directors 4 and reflector 5; obviously any other arrangement of these or similar parts may be provided on the stay 1.

Investigations made with metal masses adjacent to the dipole have proved the influence of the metal stay on the efiiciency of the dipole and to this end, I have executed two measurements for a frequency of 205.5 megacycles (middle of the channel 9) and the results obtained are as follows:

(1) The folded dipole being located at the end of the insulating stay, i.e. at about 65 cm. from the metal mast, the voltage found was equal to 2.

(2) With the folded dipole shifted to a position at 12.5 cm. from the mast, the voltage was equal to 1.86 i.e. a loss in voltage equal to 0.93 or 0.6 db.

This shows how any metal mass even extending perpendicularly to the electric field may cause a loss which is not negligible.

Various attempts have been made and certain results are given hereinafter, relating to a transmission at a small distance with a small power as provided with a conventional aerial of a general structure referred to hereinafter as A incorporated an insulated dipole and a metal stay of the three-element category for channels 8, 9, 10 and a further aerial designated by B with an insulating stay according to my invention wherein the distance from the dipole to the reflector is equal to 38.7 cm., that from the dipole to the director is 13.5 cm. while the reflector has a length of 72.6 cm., the director a length of 63.8 cm. and the dipole a length of 68.5 cm.

Aerial Volta ne for 195 Voltage for 216 me.

The calculation of the average gain of the aerial B with reference to A can be obtained as follows: Average voltage received by the aerial A:

so that the grain is equal to:

24.35/2l.45=1.135=+l.1 db

The absolute average gain of the aerial B is thus equal to whereas for the aerial A, it is equal to i.e. +5.3 db.

These results have been checked through measures made on a real transmitter since the different conditions of polarisation of the waves and of parasitical reflection may lead to ditferences between the calculated gains and the gains which are actually available for the operator when receiving television waves from the transmitter.

Two measurements have been made with each of the above-mentioned aerials A and B by means of a field measuring instrument of the Rohde and Schwarz brand.

With the aerial A sold in trade, the voltages found were as follows:

(a) for the French-speaking Belgian television system: 13.47.

(b) for the Flemish-speaking Belgian television system: 10.61.

The same measurements executed with my improved aerial B provide the following voltage values:

(a) for the French-speaking Belgian television system: 16.1 1.

(b) for the Flemish-speaking Belgian television system: 14.

These measurements provide finally as a relative gain for the aerial B with reference to the aerial A:

(a) for the French-speaking Belgian television system:

Thus the gain is equal to about an average of 2 db over the result obtained with the aerials presently sold in trade.

Moreover a rate of standing waves which is clearly lower in the case of my improved aerial B shows that the impedance is better matched so that the operator can rely upon the benefit of a more stable synchronization of the pictures.

I have also proceeded with measurements on the aerials A and B of the capacity between the dipole and the mast.

To execute such measurements, I have resorted to the so-called Component Bridge produced by the Wayne Kerr Laboratories Ltd. which measuring bridge has the fortunate property of allowing measurements of even very low impedances in situ.

In the case of the aerial A the capacity between the dipole and the mast is equal to 6.8 micrornicrofarads.

The same measurements made on the aerial B provided with an insulating stay have given a capacity of 1.1 picofarad.

This results in a complete confirmation of my calculations and shows that when operating on broadcast waves the losses due to the presence of the mast will be six times lower in the case of the aerial B than in the case of the aerial A.

Obviously, my invention has been described and illustrated by way of a mere exempliflcation and by no means in a binding sense and various and numerous modifications may be brought to its execution without unduly widening the scope of the invention as defined in the accompanying claims.

What I claim is:

1. An aerial chiefly for television and frequency modulated broadcast waves, comprising, a mast; a transverse stay carried by said mast and consisting of polyester material; and a plurality of aerial elements mounted on said stay and comprising at least one dipole, at least one reflector and at least one director, all said elements extending transversely of said stay, said reflector and said director being spaced in opposite directions from said dipole distances related to the wave length to be received, whereby said stay is effective to prevent leakage between the antenna elements, and to prevent reflection of said waves from said stay toward said aerial elements, for providing a relative optimum in directional gain, in front to back ratio, and in band width.

2. An aerial chiefly for television and frequency modulated broadcast waves, comprising, a mast; a transverse stay carried by said mast and consisting of polyester material and said material having water repellent surface characteristics; and a plurality of aerial elements mounted on said stay, comprising at least one dipole, at least one reflector and at least one director, all said elements extending transversely of said stay, said reflector and said director being spaced in opposite directions from said dipole distances related to the wave length to be reoeived, whereby said stay is effective to prevent leakage between the antenna elements, and to prevent reflection of said waves from said stay toward said aerial elements, for providing a relative optimum in directional gain, in front to back ratio, and in band width.

3. An aerial chiefly for television and frequency modulated broadcast waves, comprising, a mast; a transverse stay carried by said mast and consisting of polyester material; a plurality of aerial elements mounted on said stay, comprising at least one dipole, at least one reflector and at least one director, all said elements extending transversely of said stay, said reflector and said director being spaced in opposite directions from said dipole distances related to the wave length to be received, whereby said stay is effective to prevent leakage between the antenna elements, and to prevent reflection of said waves from said stay toward said aerial elements, for providing a relative optimum in directional gain, in front to back ratio, and in band width; and means attaching said stay to said mast at a point of zero ground potential located in spaced relation between two of said aerial elements.

4. An aerial chiefly for television and frequency modulated broadcast waves, comprising, a mast; a transverse stay carried by said mast and consisting of polyester material; a plurality of aerial elements mounted on said stay, comprising at least one dipole and at least one reflector, all said elements extending transversely of said stay, said reflector being spaced from said dipole a distance related to the wave length, whereby said stay is effective to prevent leakage between the antenna elements, and to prevent reflection of said waves from said stay toward said aerial elements, for providing a relative optimum in directional gain, in front to back ratio, and in band width.

5. An aerial chiefly for television and frequency modulated broadcast waves, comprising, a mast; a transverse stay carried by said mast and consisting of polyester material; a plurality of aerial elements mounted on said stay, comprising at least one dipole and at least one reflector, all said elements extending transversely of said stay, said reflector being spaced from said dipole a distance related to the wave length, whereby said stay is effective to prevent leakage between the antenna elements, and to prevent reflection of said waves from said stay toward said aerial elements, for providing a relative optimum in directional gain, in front to back ratio, and in band width; and means attaching said stay to said mast at a point of zero ground potential located in spaced relation between two of said aerial elements.

References Cited in the file of this patent UNITED STATES PATENTS 2,213,276 Gossel Sept. 3, 1940 2,486,872 Parker Nov. 1, 1949 2,523,531 Flippen Sept. 26, 1950 2,582,634 Jones Jan. 15, 1952 2,589,174 Wargo Mar. 11, 1952 2,619,596 Kolster Nov. 25, 1952 2,661,423 Middlemark Dec. 1, 1953 OTHER REFERENCES The American Radio Relay League, Inc., fourth edition, second printing, April 1947, (Copyright 1946), Chapter 117, Pp- 117 and 127-129.

Television Antennas (Nelson), published by Howard Sams, May 1949, pages 69 and 139 to 142.

7 Patent No. 3,017,632

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION January 16, 1962 Gustave Jean Henri Joseph Bernard It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below.

In the grant, lines 1 and 12, and in the heading to the printed specification, line 5,' for "Gustave Jean Henri Josep", each occurrence, read Gustave Jean Henri Joseph Bernard This certificate supersedes Certificate of Correction issued May 29, 1962.

Signed and sealed this 23rd day of October 1962.,

(SEAL) Attest:

DAVID L. LADD ERNEST w. SWIDER A e g Office! Commissioner of Patents 

